The present embodiments relate to semiconductor device fabrication and are more particularly directed to clean-up processing following photoresist patterning and etching of a low-dielectric constant material.
Integrated circuit technology continues to advance at a rapid pace, with many circuit technologies being implemented using semiconductor fabrication processes. With the advancement of semiconductor circuit fabrication, consideration is given to various aspects, including maximizing efficiency, lowering manufacturing cost, and increasing performance. With these goals in mind, low dielectric constant materials are now being considered as favorable for various insulating layers, sometimes referred to as interlevel dielectrics, used in a semiconductor circuit. In the past, such insulating layers were implemented using silicon dioxide (i.e., SiO2). Silicon dioxide has a dielectric constant, sometimes referred to in the art by the value k, on the order of 4.0. However, relatively lower dielectric constant values, such as on the order of 2.7 or 2.8, are now achieved by incorporating carbon within the silicon dioxide, thereby creating what is referred to in this document as a carbon-containing oxide. Carbon-containing oxides are sold under various trade names, such as organo-silicon glass (“OSG”) commercially available from Novellus and black diamond commercially available from Applied Materials. Carbon-containing oxides may contain a considerable amount of carbon, such as on the order of 20 to 30 atomic percent (i.e., amount of carbon per atomic volume). The inclusion of the carbon drives down the dielectric constant which is a highly desirable goal. Specifically, by reducing the dielectric constant, such as is achieved by these carbon-containing oxides, semiconductor devices may be constructed using thinner films for insulating layers. This approach decreases device size and cost. Performance is also increased, such as by way of example where metal lines (e.g., copper) are formed closer together due to the thinness of the low-dielectric constant carbon-containing oxide which separates the metal from other layers/regions/devices.
While carbon-containing oxides have advanced various goals in the formation of semiconductor circuits, the present inventors have observed a considerable drawback in the use of such low dielectric constant (known as low k) materials. Specifically, during the formation of semiconductor circuits, and as also detailed later, it is known in the art to use photoresist materials as a mask for etching through an insulating layer, such as a silicon dioxide layer, to provide for example, vias, trenches, or other areas through which electrical contact may be made to various points covered by the insulating layer. Once the photoresist has served its masking purpose, it along with any related residue is removed. This process is sometimes referred to as a clean-up or a strip, and such removal has been achieved in the art by various different processes. However, the present inventors have observed that these traditional photoresist-removal processes, while effective for ordinary silicon dioxide, negatively affect a lower dielectric constant material such as a carbon-containing oxide. For example, one prior art photoresist-removal process uses an oxygen-based plasma at high temperature, that is, on the order of 250° C. However, when used with a carbon-containing oxide, the prior art use of an oxygen-based plasma causes the oxygen in the plasma to react with the carbon-containing oxide; in other words, rather than being inert with the carbon-containing oxide as is desired, the oxygen may cause the carbon-containing oxide to convert (lose carbon) in part and/or to diminish in width and/or in depth. Further complicating this issue is that manufacturers provide carbon-containing oxides that contain different percentages of carbon. As a result, the present inventors have observed a corresponding difference in the rate of carbon loss and width and/or depth loss of the carbon-containing oxide when the film is exposed to oxygen-containing plasma. For example, in the past rates of degradation were observed on the order of 25 Angstroms per minute exposure to oxygen-containing plasmas while more recently rates of degradation on the order of 100 Angstroms per minute have been observed. Thus, there is a need to reduce this degradation, and indeed such a need will continue should low k materials continue to show degradation on reaction with standard (e.g., O2, 250° C.) photoresist removal processes.
In view of the above, there arises a need to address the drawbacks of the prior art and to provide a method for effectively removing post-etch polymers and photoresist from low dielectric constant materials, as is achieved by the preferred embodiments described below.